Many materials are known as oxide films used for thin film elements in thin film integrated devices, which are formed by oxidization through the anodic oxidation of a metal thin film layer of tantalum, titanium or aluminum, etc. capable of anodic formation formed by the sputtering or the vacuum evaporation method; or by reactive sputtering of the metal in an inert gas containing oxygen; or by directly sputtering the oxides of the above metals in an inert gas.
These oxide films often play a basic role of the function of the thin film elements. The characteristics of the oxide films themselves influence the qualities of those of the respective thin film elements. For example, in thin film condensers, anodic oxidation films of tantalum, aluminum, etc. are well known.
Recently, a method of forming a hybrid integrated circuit comprising thin film resistors and thin film condensers has been intensively studied, according to which a thin film alloy of tantalum and aluminum, occasionally doped with nitrogen, is formed by a sputtering method and a part of the film is anodic oxidized (see for example Thin Solid Films, 109 (1983) 339-343). However, the manufacturing process using the anodic oxidation method is not only complicated, but also inevitably needs the provision of current paths for the anodic formation. When the method is applied to the thin film integrated devices, integration is difficult because the freedom of designing a pattern is limited.
The above-mentioned thin film of tantalum-aluminium alloy has a high resistivity. When a thin film condenser is formed by anodic oxidation, the dielectric loss (tan .delta.) becomes large at high frequencies and the usable frequency band is reduced. Furthermore, since the interface between the anodic oxidation film and the electrode does not become perfect oxide, the breakdown field intensity (Eb) of the condenser becomes small. On the other hand, tantalum oxide formed by the sputtering method has many pinholes and hence the leakage current is large. Since the breakdown field intensity Eb is also low (about 1.5.times.10.sup.6 V.cm.sup.-1), the film thickness should be made large. This makes it difficult to obtain a large capacitance element. Even aluminum oxide formed by the sputtering method has a small dielectric constant (.epsilon.r) and cannot form a large capacitance element.
Thin film transistars have been intensively studied as a driver for liquid crystals and EL display devices, etc., in which an on-off ratios of current is desired. For this purpose, the gate oxide film should have a large dielectric constant (.epsilon.r) to increase the mutual conductance (gm) and a small leakage current to decrease the off-current. Furthermore, in order to obtain a thin film transistor with a stable characteristic, it is desirable that the characteristics of the interface between the semiconductor layer and the gate oxide film are good.
The thin film light emitting element is represented by a thin film EL (electroluminescence) element using a ZnS:Mn emission layer. The field intensity for obtaining the EL emission is high, about 10.sup.6 Vcm.sup.-1. An EL thin film element with a high brightness is desired, in which the electric field is applied efficiently to the emission layer and which has a low threshold voltage for light emission and can operate with a low voltage. For this purpose, it is required that the oxide film provided on the both sides or on one side of the emission layer has a large dielectric constant (.epsilon.r), a high breakdown voltage and a low leakage current.
An EL display device of matrix type is constituted with thin film EL elements, thin film transistors and thin film condensers, etc. Therefore, in order to increase the reliability, the oxide films used in these elements should have the above-mentioned characteristics. This is also the case with a liquid crystal display device of matrix type.